The present invention relates to an image processing apparatus, and more specifically to an image processing apparatus for three-dimensional computer graphics such as that used in work stations or game machines, which image processing apparatus can output image signals in accordance with image information of a polygon in realtime.
An image processing apparatus herein described is an apparatus which can output image signals to be provided to a display apparatus such as a CRT display in accordance with input from external devices. Such an image processing apparatus can output not only image signals for a two-dimensional image but also image signals for a pseudo three-dimensional image by synthesizing two dimensional image signals. Therefore, such an image processing apparatus is widely used in TV game machines or computer graphics apparatuses in which a three-dimensional image display is adopted.
A conventional image processing apparatus of this kind uses a bit map display method (graphic display). In order to use a bit map display method, a bit map memory having memory areas is provided, each of which memory areas stores all pixel signals included in an entire single image to be displayed on a CRT. When a picture is displayed in, for example, computer graphics, a contour of a polygon is drawn on a display, and then the inside of the polygon is painted. Accordingly, there is a problem in that if the number of polygons is increased, a memory having a large capacity is required and a realtime image processing is not performed.
Japanese Laid-Open Patent Application No. 62-231379 discloses a picture synthesizing apparatus in which image signals are synthesized and output in realtime in accordance with supplied contour line information of a picture.
In a field processor of the above-mentioned picture synthesizing apparatus, polygons are processed, in turn, by means of digital differential analysis (DDA), and then the results of the operation are stored in a memory. The memory is required to have a capacity, when the processing of all polygons have been finished, sufficient for storing information for all X start points and all X end points lying on a single scan line and for storing additional information by which attributes of the polygons can be recognized. Accordingly, the capacity of the memory has to be relatively large, and thus the cost of the memory is increased. In particular, the greater the amount of additional information for polygons, the greater the amount of memory capacity that is required. Therefore, there is a problem in that the proportion of the cost of the memory regard to the total manufacturing cost of the apparatus is greatly increased.